PLEASE NOTE: In mid 1954 Rolex went back to 100,000 instead of 1,100,000 on case numbers for the Oyster watch.

When Rolex reached the 999,999 production serial number in the early 1950s they restarted the production serial numbers at 100,000 rather than begin a 7 digit number at 1,000,000. During this period Rolex was also putting a date code on the inside of the case backs, so confusing serial numbers can sometimes have their production date determined. Look for the Roman numeral I, II, III, or IV for the quarter and two Arabic numerals for the year (e.g. IV55 is the 4th quarter of 1955).

In the late 1950s, Rolex again reached the 999,999 number and they started their 7 digit numbering system at 1,000,000 for production serials. This continued until the 1990s when production serials reached 9,999,999.

Rather than begin an 8 digit production serial, Rolex instead began their serials with a letter prefix such as R, L, E, and X (ROLEX without an O which could be mistaken for a zero). N, C, and S came out during the early to mid 1990s. W, T, and U came a little later. The latest letter prefixes are all running concurrently. Only Rolex knows the exact date that any watch was actually produced.

Rolex model numbers are four, five, or six digits. The first two or three numbers describes the type of watch. With five digit model numbers, the fourth number describes the type of bezel (with some exceptions) and the fifth number describes the material from which the case is made.